How Green is that Fuel-Efficient Car?

Here are two facts that irk almost all automobile operators: The first is that putting gas in your car is expensive. Gas prices average $3.29 per gallon across the country, with prices shooting past $4 in many places. The second fact is that burning gas to drive your car is bad for the earth, with transportation accounting for 13% of global greenhouse gas emissions.

Car advertisers, being experts on cars, know these two facts drive many consumers towards vehicles billed as fuel-efficient and zero-emission. Drivers want cars they can put less gas into and cars that spit out fewer icky things.

But green car claims aren’t always entirely truthful. Here’s what savvy consumers should know about green terminology.

What comes out of the car: “Zero Emissions”

Car emissions are an increasing national concern. In October, eight states pledged to work together to put 3.3 million zero-emission vehicles on their roads over the next 12 years, a move the states hope will cut down on pollution.

But is there even such a thing as a zero-emission car? Perhaps not. While the FTC has ruled that car companies can claim zero-emissions provided they produce zero tailpipe emissions, electric cars are generally charged on the public grid, and the public grid is powered by fossil fuels burned at power plants. And while electric cars use fossil fuel power more efficiently – because large power plants burn fuel more effectively than individual small car engines – the process of burning gas and coal still produces pollution. An electric car charged on a grid that is powered by wind or solar energy would be emissions-free. But unless an electric-car owner also owns a wind farm, that scenario is unrealistic. (A true zero-emission vehicle doesn’t quite look like what any car dealer is selling.)

French automaker Renault got into trouble with the ASA after running ads in the U.K. for its electric cars, which it claimed to be zero-emission vehicles. After reviewing the public objections to the ads, the The Advertising Standards Authority (ASA) is a self-regulatory body that monitors advertising in the United Kingdom. ruled, “because driving the vehicle would result in CO2 emissions if charged from conventional energy sources, the claim the vehicle had ‘zero emission(s)’ was misleading.” Renault was banned from running the ads again in the U.K.

Yet automakers in both the U.S. and U.K. continue to advertise their vehicles as “zero-emissions.” Nissan’s website makes zero-emissions claims on both sides of the Atlantic.

What goes in: Miles-per-gallon

Car companies have been advertising their vehicles’ mpg-ratings since at least the ‘70s, attempting to attract consumers concerned about gas prices or the environment. Chevrolet has been promoting cars that get 30 mpg for at least forty years. (Compare this ad from the 1970s with this ad from the 2000s.) In recent years, some auto makers have gotten into hot water for advertising false mileage claims. Ford offered refunds to appease consumers after reducing the estimated mpg on its C-Max hybrid earlier this year.

The push for fuel-efficiency goes all the way to the top. Last year, the U.S. government set higher standards for fuel economy going forward. Auto-makers’ fleets of cars and light trucks must, when averaged together according to sales, have a combined (highway and city) mpg rating of 35.5 by 2016, and 54.5 by 2025.

But these improvements may sound bigger than they really are. A 2008 Science magazine article argued that a different measurement, gallons-per-1,000-miles, actually gives consumers a better understanding of fuel consumption, as traditional mpgs can be misleading. (In Europe, the metric cousin liters-per-100-kilometers has long been the standard for measuring fuel efficiency.)

The problem with miles-per-gallon, per phsy.org:

People presented with a series of car choices in which fuel efficiency was defined in miles per gallon were not able to easily identify the choice that would result in the greatest gains in fuel efficiency.
For example, most people ranked an improvement from 34 to 50 mpg as saving more gas over 10,000 miles than an improvement from 18 to 28 mpg, even though the latter saves twice as much gas. (Going from 34 to 50 mpg saves 94 gallons; but from 18 to 28 mpg saves 198 gallons).

In other words, a consumer saves more gas (and money) by switching from a gas-guzzling monster truck (10 mpg) to an inefficient sports car (20 mpg) than a consumer switching from that same sports car (20 mpg) to a hybrid car (50 mpg). Over 1,000 miles, the monster-truck-to-sports-car swap saves $200; the sports-car-to-hybrid swap saves only $120.

The fuel-economy stickers required on cars starting this year still list mpg as the standard for measuring fuel economy, but gallons-per-100-miles is listed below in a smaller font.

Consumers concerned about gas usage and fuel emissions can still find cars that are better for their wallets and the earth. An electric car getting 100 mpg is certainly better than a monster truck getting 10 mpg. But understanding what “zero-emissions” and mpg really means can help consumers make smarter car-buying choices.